Core A: The Neuropathology and Cell Culture Core The Neuropathology and Cell Culture Core is the scientific core of this Program Project Grant (PPG). The central role of this Core is to assist the overall objectives of the three research projects within the PPG to determine the different molecular pathways involved in the development of HIV encephalitis in AIDS patients. The Neuropathology and Cell Culture Core will assist the participants of the Program Project by providing surgical and autopsy brain tissue material from HIV-1 infected patients diagnosed with HIV encephalitis, as well as brains from HIV-1 infected individuals with no CNS involvement and normal control brains. In close collaboration with Projects 1, 2 and 3, we will perform immunohistochemical analysis, including double labeling, of viral proteins, cellular markers, and the different downstream molecules of the Rho/Rac pathway and their association with Pur-a (Project 1), the TNFa and Ras pathway and its association with the IGF- 1/IRS pathway (Project 2), and the HIF-1 pathway and its association with Vpr (Project 3). The Neuropathology and Cell Culture Core will also provide highly purified cultures of human fetal microglia, astrocytes, and neurons on demand. Primary cultures of neurons will be prepared from rat and mouse hippocampus for the proposed studies. Established cell lines, such as PC12 will be maintained, cultured, and distributed to the projects. Also, Conditioned Media from HIV-1 infected cells will be prepared for use by the individual projects. Finally, the Core will provide cultures of neurospheres differentiated into different cellular phenotypes, including neurons, oligodendrocytes and astrocytes. The proposed experiments will aid Projects 1, 2 and 3 to decipher the molecular pathways involved in the pathogenesis of HIV encephalitis.